Processing methods and processing apparatus

ABSTRACT

A method and apparatus for processing a material are provided, the material being the upper layer from a metal melting process, the material containing one or more salts, the material containing one or more metals, the salts and/or metals being recycled as a result of the method/apparatus. The method includes feeding the material to a leaching step; obtaining a leachate from the leaching step; feeding the leachate to a drying step or spray drying step; obtaining a solid from the drying step or spray drying step. Off gases from the leaching step are used to provide heat to the drying step. The drying step provides a product well suited to being turned into pellets for reuse.

This application is a National Stage of International Application No.PCT/GB2014/053129, filed Oct. 20, 2014, and entitled IMPROVEMENTS IN ANDRELATING TO PROCESSING METHODS AND PROCESSING APPARATUS, which claimsthe benefit of GB 1318468.4, filed Oct. 18, 2013. This applicationclaims priority to and incorporates herein by reference theabove-referenced applications in their entirety.

This invention concerns improvements in and relating to processingmethods and apparatus, particularly for processing slags to recover oneor more useful components thereof.

Furnaces handling molten aluminium, for example, are provided with asalt barrier on top of the molten metal to reduce oxidisation and/orpromote the removal of contaminants from the molten metal. The saltbarrier effectively becomes part of the slag as a result of the process,after which it is commonly referred to as a salt slag. There areadvantages in processing this material once removed from the furnace.The advantages include the recovery and reuse of one or more of thecomponents and/or a reduction in the hazards the slag presents.

Existing approaches tend to use centralised processing plants to takethe cold slag and reprocess it. This causes transport issues in terms ofcost and transport footprint and has a negative impact upon thesubsequent processing and products.

The invention has amongst its possible aims to facilitate processing ofthe slags, economically at the same site it is produced at. Theinvention has amongst its possible aims to reduce costs involved in theprocessing. The invention has amongst its potential aims to giveimproved products, potentially in terms of their value and/orusefulness.

According to a first aspect there is provided a method of processing amaterial, the method including:

a) feeding the material to a leaching step;

b) obtaining a leachate from the leaching step;

c) feeding the leachate to a spray drying step;

d) obtaining a solid from the spray drying step.

The method may include the further step of compressing and/or mouldingthe solid into pellets.

The method may include 1) providing a material on the surface of amolten metal in a furnace, the furnace being at a first location; 2)removing the material from the furnace; 3) processing the materialremoved from the furnace at a second location, the second location being5 km or less from the first location and the processing including one ormore of steps a), b), c) or d). The method may include one or more ofthe processes at the second location being applied before thetemperature of the material removed from the furnace has reduced below100° C., preferably below 350° C., more preferably below 525° C. and yetmore preferably below 760° C.

According to a second aspect there is provided apparatus for processinga material, the apparatus including:

a) leaching apparatus;

b) a feeder providing material to the leaching apparatus;

c) an outlet for leachate from the leaching apparatus;

d) a spray dryer;

e) the outlet being fluidly connected to the spay dryer;

f) an outlet from the spray dryer for solids.

The apparatus may include the compression and/or moulding apparatus forproducing pellets and/or a feeder for providing a solid obtained fromthe leachate to the compression and/or moulding apparatus.

The apparatus may include 1) a furnace, the furnace being at a firstlocation; 2) a feeder for introducing a material to the surface of amolten metal in the furnace; 3) one or more processors for the materialremoved from the furnace, the one or more processors being provided at asecond location, the second location being 5 km or less from the firstlocation and the one or more processors including one or more of theprocessors in one or more of features a), b), c), d), e) or f).

According to a third aspect there is provided a method of processing amaterial, the method including

-   -   a) feeding the material to a leaching step;    -   b) obtaining a leachate from the leaching step;    -   c) obtaining a solid from the leachate;    -   d) compressing and/or moulding the solid into pellets.

The method may include feeding the leachate to a spray drying step,preferably to obtain the solid for the compressing and/or moulding step.

The method may include 1) providing a material on the surface of amolten metal in a furnace, the furnace being at a first location; 2)removing the material from the furnace; 3) processing the materialremoved from the furnace at a second location, the second location being5 km or less from the first location and the processing including one ormore of steps a), b), c) or d). The method may include one or more ofthe processes at the second location being applied before thetemperature of the material removed from the furnace has reduced below100° C., preferably below 350° C., more preferably below 525° C. and yetmore preferably below 760° C.

According to a fourth aspect there is provided apparatus for processinga material, the apparatus including:

a) leaching apparatus;

b) a feeder providing material to the leaching apparatus;

c) an outlet for leachate from the leaching apparatus;

d) compression and/or moulding apparatus for producing pellets;

e) a feeder for providing a solid obtained from the leachate to thecompression and/or moulding apparatus.

The apparatus may include a spray dryer and/or the outlet being fluidlyconnected to the spray dryer and/or an outlet from the spray dryer forsolids.

The apparatus may include 1) a furnace, the furnace being at a firstlocation; 2) a feeder for introducing a material to the surface of amolten metal in the furnace; 3) one or more processors for the materialremoved from the furnace, the one or more processors being provided at asecond location, the second location being 5 km or less from the firstlocation and the one or more processors including one or more of theprocessors in one or more of features a), b), c), d) or e).

According to a fifth aspect there is provided a method of processing amaterial, the method including

a) providing a material on the surface of a molten metal in a furnace,the furnace being at a first location;

b) removing the material from the furnace;

c) processing the material removed from the furnace at a secondlocation, the second location being 5 km or less from the first locationand the processing including one or more steps selected from:

-   -   1) reduction of the size of a mass of the material;    -   2) leaching the material to provide a leachate;    -   3) spray drying one or more components, such as a leachate, to        provide a solid;    -   4) compressing or moulding a solid, for instance the solid        obtained from a leachate, to provide pellets.

The method may include one or more of the processes at the secondlocation being applied before the temperature of the material removedfrom the furnace has reduced below 100° C., preferably below 350° C.,more preferably below 525° C. and yet more preferably below 760° C.

The method may include feeding the leachate to a spray drying step,preferably to obtain the solid for the compressing and/or moulding step.

The method may include the further step of compressing and/or mouldingthe solid into pellets.

According to a sixth aspect there is provided apparatus for processing amaterial, the apparatus including

a) a furnace, the furnace being at a first location;

b) a feeder for introducing a material to the surface of a molten metalin the furnace;

c) one or more processors for the material removed from the furnace, theone or more processors being provided at a second location, the secondlocation being 5 km or less from the first location and the one or moreprocessors including one or more processors selected from:

-   -   1) a breaker for reducing of the size of a mass of the material;    -   2) leaching apparatus;    -   3) spray drying step apparatus;    -   4) compression or moulding apparatus for a solid, for instance        the solid obtained from a leachate from the leaching apparatus,        to provide pellets.

The first and/or second and/or third and/or fourth and/or fifth and/orsixth aspects of the invention may include any of the features, optionsor possibilities set out elsewhere within this document, including fromamongst the following.

The method of processing may be processing to separate one or more saltsfrom one or more metals. For instance sodium chloride and/or sodiumchlorate and/or potassium chloride and/or potassium chlorate may beseparated, particularly from aluminium and/or ferrous metals.

The method of processing may be processing to separate one or more saltsfrom one or more non-metals. For instance sodium chloride and/or sodiumchlorate and/or potassium chloride and/or potassium chlorate may beseparated, particularly from aluminium oxides and/or other insolublenon-metallic compounds.

The method may provide for the recycling of one or more metals, forinstance aluminium. The method may provide for the recycling of one ormore salts, for instance sodium chloride and/or potassium chloride.

The material may be a slag. The material may be the upper layer from ametal melting process. The material may be a layer involved in recyclingaluminium. The material may contain one or more salts, for instancesodium chloride and/or sodium chlorate and/or potassium chloride and/orpotassium chlorate. The material may contain one or metals, for instancealuminium, and/or metal oxides, for instance aluminium oxide. Thematerial may contain 10-35% aluminium oxide, 25-60% sodium chloride,10-35% potassium chloride, 2-10% metallic aluminium and impurities, withthe combination totaling 100%, for instance 15-30% aluminium oxide,30-55% sodium chloride, 15-30% potassium chloride, 5-7% metallicaluminium and impurities, with the combination totaling 100%. Theimpurities may include carbides, nitrides, sulphides and/or phosphides.

The method of providing a material on the surface of a molten metal in afurnace may include feeding the material onto the surface of the moltenmetal, preferably from above the molten metal. The material may be fedin batches. The material may be fed continuously.

The molten metal is preferably aluminium.

The furnace may be a rotary furnace or other furnace type.

The first location may be the location at which the furnace is providedand/or at which the material is stored after removal from the furnaceand/or after being compressed.

The material may be a slag. The material may be a compressed slagproduced by compressing a slag. The slag may be compressed in a slagpress. The slag may be compressed to remove molten aluminium from theslag. The material may contain one or more salts, for instance sodiumchloride and/or sodium chlorate and/or potassium chloride and/orpotassium chlorate. The material may contain one or more metals, forinstance aluminium, and/or metal oxides, for instance aluminium oxide,ideally at a lower level than in the slag.

The compressed slag may be of a lower temperature than the slag. Thecompressed slag may have a temperature of less than 500° C. aftercompression.

The compressed slag may be allowed to cool. Preferably the compressedslag is not allowed to cool below 100° C., preferably below 350° C.,more preferably below 525° C. and yet more preferably below 760° C.

The compressed slag may be allowed to cool at the first location.

The second location may process less than 20,000 tonnes of material peryear, potentially less than 15,000 tonnes and even less than 10,0000tonnes of material per year.

The processing of the material removed from the furnace which isprovided at a second location may include one or more of the stepssubsequent to the removal of the material from the furnace and morepreferably subsequent to the compression of the material, for instanceto form the compressed slag.

The second location is 5 km or less from the first location, andpreferably is less than 2 km from the first location, more preferably isless than 1 km from the first location and ideally is less than 500 mfrom the first location. The first location and the second location arepreferably owned and/or operated by the same legal entity. The furnaceis preferably fed with recycled aluminium.

The compressed slag preferably is not allowed to cool below 100° C.,preferably below 350° C., more preferably below 525° C. and yet morepreferably below 760° C. before one or more process step are conductedat the second location.

The method may include a size reduction step. The size reduction stepmay reduce one or more dimensions of the material and/or increase thenumber of discrete parts in which the material is present. The sizereduction step may include a plurality of size reduction steps. The sizereduction step may include a crushing step. The size reduction step mayinclude a grinding step. The size reduction step may include one or moresizing steps, for instance to separate the material into one or morefractions according to size.

The method may include a ferrous and non-ferrous metal separation step.The separation may be made by an eddy current separator. The method mayinclude a metal and non-metal separation step. The separation may bemade by an eddy current separator and/or vibrating table and/orcompressed air separator. Aluminium extracted by one or both of theseseparations may be returned to the furnace.

The method may include feeding the material to a leaching step byintroducing the material to a leaching tank. The leaching step may beprovided with one or more other feeds, for instance water.

The method may include obtaining a leachate from the leaching step orsteps.

The leaching step may be a multiple pass leaching process where multiplepasses through one leaching tank are provided and/or a multiple stageleaching process where passage through a number of leaching tanks isprovided. The method may include obtaining the leachate from theleaching step or steps by extracting the leachate from a leaching tank,preferably from the bottom thereof. The leaching step may be providedwith one or more other outlet streams, for instance an off gas streamand/or non-dissolved solids stream.

The off gas stream may be further processed, for instance by beingcombusted, ideally with heat and/or power generated by the combustionbeing used in one or more of the method steps and ideally the spraydrying step.

The non-dissolved solids stream may be further processed, for instancein a solid liquid separator such as a filter. The separated solids mayform a by-product, ideally which has a market value. The separatedliquids may be returned to the leaching step and/or may be fed to thespray drying step.

The method may include feeding the leachate to a spray drying step, forinstance via one or more buffering or storage containers. The leachatemay be pumped to the spray drying step, and particularly one or multiplenozzles therein.

In relation to spray drying, one or more gases, for instance air, may bepumped to the spray drying step, particularly the nozzle/nozzlestherein. The nozzle may co-inject the gas and leachate. The nozzle mayact as an atomiser of the fluid leachate

The method may include feeding hot gas, preferably hot air, to the spraydrying step.

The gases may be the hot gases from the off gas stream processing and/ormay possess energy generated by the off gas stream processing,particularly in terms of their temperature.

The method may include obtaining a solid from the spray drying step, forinstance by separating the solid and the gas in the spray drying step.The solid may be collected at the bottom of the spray drying step. Thesolid may be removed in batches or continuously. One or more subsequentseparations of solids from gas may be provided for the gas outletstream, for instance using bag filters and/or cyclone separators. Thegas outlet stream, preferably after solids separation, may be used toagitate and/or heat in one or more of the method steps, particularly inthe drying step or spray drying step.

The method may include obtaining the solid from the leachate by usingthe spray drying step.

The method may include compressing and/or moulding the solid intopellets in one or more further steps. The one or more further steps mayinclude a pelletising step. The compressing and/or moulding may beprovided without adding any further components to the solid. Inparticular no binders or moisture may be added.

The compressed and/or moulded solids, for instance pellets, may becollected and/or stored, for instance for subsequent use. The compressedand/or moulded solids, for instance pellets, may be fed to a furnace,ideally the furnace at the first location. The compressed and/or mouldedsolids, for instance pellets, may be fed to a furnace, ideally thefurnace at the first location, to provide a material on the surface of amolten metal in a furnace.

The compressed and/or moulded solids, for instance pellets, may beproduced to a controlled size.

The compressed and/or moulded solids, for instance pellets, may beproduced to a controlled size distribution, for instance such that lessthan 5%, more preferably less than 2%, of the pelletised material byweight is less than 149 microns in diameter, for instance considered asthe largest linear dimension.

The compressed and/or moulded solids, for instance pellets, may beproduced to a controlled moisture level, for instance less that 0.5 wt %or preferably less than 0.2 wt %.

The compressed and/or moulded solids, for instance pellets, may beproduced with a controlled ratio of sodium chloride to potassiumchloride, for instance a predetermined ratio +/−5%. The ratio may bebetween 4:1 and 1:1 sodium chloride to potassium chloride.

One or more batches of compressed and/or moulded solids, for instancepellets, having a first set of characteristics may be blended with oneor more other batches of compressed and/or moulded solids, for instancepellets, having one or more different characteristics.

Various embodiments of the invention will now be described, by way ofexample only, and with reference to the accompanying drawings in which:

FIG. 1 is a flow diagram for a process for the recovery of salt from analuminium recycling process, including improvements according to theinvention;

FIG. 2 is a flow diagram for a process according to an embodiment of theinvention;

FIG. 3 is a schematic illustration of a spray dryer for use in theinvention.

There are various problems with the large scale centralised process.These include:

The transport costs in taking the compressed slag 9 to a suitablecentralised plant for processing;

The significant regulatory issues (particularly if country borders arecrossed) with such transportation;

The safety risk from accidents and the like involved in suchtransportation;

Having to use a centralised process plant, outside of the saltproducer's control;

The increased energy requirements and difficulty in achieving sizereduction of the cold compressed slag;

The variable nature of the feed slag, due to its containing differentsalt levels, different slat proportions, different contaminants and thelike as it arrives from various different aluminium recyclers, givingprocess control issues;

The variable nature of feed slag impacting upon the dry salt produced(in terms of its chemical make up, moisture content and sizedistribution) meaning the product is not well controlled or defined andso impairs it as a good salt feed for the furnace.

In FIG. 1, a rotary furnace 1 is used to recycle aluminium, such asscrap which is contaminated with paint, lacquers and the like. Thefurnace 1 generates an aluminium product stream (not shown) togetherwith an off gas stream 3 and a slag stream 5.

The off gas stream 3 is subjected to suitable processing to recover/useor render safe the gases it contains.

To prevent oxidisation of the aluminium and to provide other benefits, asalt is added to the top of the melt in the furnace 1 to form a barrier.The salt, together with some aluminium, forms the slag and hence theslag stream 5. The salt is mainly sodium chloride, but with potassiumchloride too and other materials. A typical salt slag (also known asaluminium salt cake) produced by the secondary aluminium industry maycontain 15-30% aluminium oxide, 30-55% sodium chloride, 15-30% potassiumchloride, 5-7% other materials (such as aluminium and impuritiesincluding carbides, nitrides, sulphides and phosphides etc.

After processing, the aluminium is drained from the furnace 1 and theslag is the main material remaining. The slag is formed mainly of thesalt, together with the removed contaminants and other components pickedup in the melting process.

When the slag stream 5 is removed from the furnace 1 it is generalemptied into bins (not shown) and then fed to a slag press 7 to allowfor mechanically assisted agglomeration of the aluminium from the slag.The aluminium is generally returned to the furnace 1 after separation.The compressed material from the slag press 7 is classified ascompressed slag 9.

The compressed slag 9 is allowed to cool. The compressed slag 9 stillcontains a material amount of aluminium and a large amount of salt. Thecompressed slag is classified as a hazardous material, with respect toenvironmental and other laws, in many countries and so requires furtherconsideration.

One option is to transport the compressed slag 9 to a suitable plant forthe recovery of the aluminium and treatment to recover the salt. Thisinvolves road transportation of the compressed slag 9 from the site ofthe furnace 1 where the compressed slag 9 is generated, to the distantprocessing plant. This involves significant transport costs, significantregulatory issues (particularly if country borders are crossed) and asafety risk from accidents and the like.

The typical process plants are large installations which providecentralised treatment of the compressed slag 9 arising from variousaluminium melting plants.

The compressed slag 9 is cold by the time processing starts and is fedto a salt crusher 11 to reduce the compressed slag 9 in size. The coldnature of the compressed slag 9 presents difficulties and increasedenergy requirements for the size reduction steps. For instance,pneumatic breakers may be needed to initially break up the compressedslag 9 into smaller lumps. The size reduction may include theillustrated salt crusher 11, together with size based separation steps,such as sieves.

The size reduced salt stream 13 is then fed to an eddy current separator15. This generates a ferrous stream (not shown) which is recycled, analuminium stream 17 which may be collected and sold and/or may bereturned to the furnace 1 and a cleaned salt stream 19.

The cleaned salt stream 19 is fed to a leaching tank 21, together with awater stream. The leaching process dissolves the salt content of thecleaned salt stream 19, ionises the sodium chlorate and so provides adissolved salt stream 23. The remaining solids, generally aluminiumoxides and non-metallic particles form suspended solid stream 25. Theleaching off gas stream 27 is fed to a combined heat and power unit 29where it is burnt to provide power and heat to the overall process, inparticular to the steam dryer 31. Typical gases include hydrogen,methane, and ammonia. Phosphine and hydrogen sulphide may also bepresent.

The suspended solid stream 25 is fed to a filter 33 to separate thesolids from the liquid. The solids are a useful by product of theprocess which can be sold. The liquids are returned (not shown) to theleaching tank 21.

The dissolved salt stream 23 is passed to an evaporator 35 to give riseto a steam stream 37, a gas hydrocarbon stream 39 (which also goes tothe combined heat and power unit 29) and a wet salt stream 41.

The steam stream 37 is fed to a condenser 43 and the resulting condensedwater stream is fed back to the leaching tank 21.

The wet salt stream 41 is taken to a super heated steam dryer 31. Thisproduces a steam/water vapour stream (not shown) which is returned tothe leaching tank 21 and the products stream, the dry salt stream 43.The dry salt stream 43 can provide salt feed 45 for the furnace 1.

The present invention attempts to address these issues and/or provideimprovements in them as a result of the process approach and changesmade.

Referring to FIG. 2, the overall process of an embodiment of theinvention is provided. Once again, the rotary furnace 51 is used torecycle aluminium and the furnace 51 generates an aluminium productstream (not shown) together with an off gas stream 53 and a slag stream55.

Features in common with the approach of FIG. 1 are not repeated, but arestill applicable to the FIG. 2 embodiment. For instance, the off gasstream 53 is subjected to suitable processing to recover/use or rendersafe the gases it contains.

The slag stream 55 is removed from the furnace 51 it is then fed to aslag press 57. The compressed material from the slag press 57 is againthe compressed slag 59.

In this embodiment of the invention, the compressed slag 59 is processedat the same site as it is generated at. This is possible because of thelower capital cost and lower unit sizes viable for the overall processselected in this embodiment when compared with the prior approach. Atypical localised plant might be configured to handle 1 tonne or lessper hour of salt, whereas centralised plants may handle 5 or more tonnesper hour.

A first benefit arising from this is that the compressed slag 59 is onlyallowed to cool to the desired extent. That cooling still aids handlingand reduces the risk of the hot aluminium reacting further, but thecompressed slag 59 is not allowed to cool to an extent that would causenegative impacts in the subsequent size reduction stage.

The compressed slag 59 is fed to a slag crusher 61 to reduce thecompressed slag 59 in size. However, as the compressed slag 59 is notcold and hard, the size reduction is easier to achieve and the sizedistribution resulting is more readily controlled. This gives a bettersize distribution and/or reduced amount of fine material, for instancesub 1 mm material. This is significant in improving the saleability ofthe solids recovered from the suspended solids stream 75.

After size reduction, the size reduced slag stream 63 is then fed to aneddy current separator 65. This generates a ferrous stream (not shown)which is recycled, an aluminium stream 67 which is returned to thefurnace 1 and a cleaned salt stream 69.

The cleaned salt stream 69 is fed to a leaching tank 71, together with awater stream 73. The same general leaching process is provided.

The known nature of the slag 59, because the aluminium recycling plantoperator and the slag processing plant operator is the same, mean thatthe feed material to the leaching tank 71 is better known and moreconsistent.

The dissolved salt stream 73, the suspended solid stream 75 and theleaching off gas stream 77 arise as before. The leaching off gas stream77, however, is now made use of to increase the energy efficiency of theoverall system. The leaching off gas stream 77 is fed to a combined heatand power unit 79 where it is burnt to provide power and heat to theoverall process. In particular, the power can be made of throughout theprocess to drive one or more processes and the heat can be made use ofin the spray dryer 97. Typical gases present include hydrogen, methane,and ammonia.

The suspended solid stream 75 is fed to a filter 83 to separate thesolids from the liquid. The solids are a useful by product of theprocess which can be sold and with improved properties and hence value,as mentioned above.

The dissolved salt stream 73 is then subjected to different processingsteps than before.

The dissolved salt stream 73 passed to the spray dryer 97, described inmore detail below. The spray dryer benefits from heat recycled from thefurnace 51 and/or from the combined heat and power unit 59. The saltstream 91 arising is much drier than from the evaporator in the FIG. 1form.

In an embodiment not shown, the dissolved salt stream 73 may be passedto an evaporator to give rise to a steam stream, a gas hydrocarbonstream (which also goes to the combined heat and power unit 79) and awet salt stream 73 which then passes to the spray dryer 97 describedabove. An issue with the salt stream 91 is that the particle size isrelatively small. However, the applicant has identified that this issuecan be address by feeding the salt stream 91 to a pelletiser 99,described in more detail below. Furthermore, the applicant hasidentified that the salt stream properties and size are ideally suitedto pelletisation without the need for further treatment or additives,such as binders.

As the product stream, the dry salt stream 93 is now pelletized, thisallows for the optimisation of the physical properties, such as the sizeof the pellets, for the subsequent reuse of the dry salt stream 93 as asalt feed 95 for the furnace 51.

In addition, the pellets are known to be of a standard content and sooffer more controlled feeds to the furnace 51, for instance in terms ofthe ratio of sodium chloride to potassium chloride present (which isused to control the sodium chloride melting temperature). The blendingof different pellets is also possible to provide other variation in thefeed to the furnace 51.

Finally, the pellets are also more suited to storage, without moisturetake up, for instance, than the dry salt product of the FIG. 1 form.

As illustrated in FIG. 3, the spray dryer 97 receives the dissolved saltstream 73 via a balance tank 200, with the flow into the tank controlledby a valve 202 to maintain the solution level. Low to open and high toclose level probes are used to operate the valve 202. A water inlet 204is also provided to the balance tank 200. The outlet 206 supplies thedissolved salt stream 73 to a peristaltic pump which pumps the dissolvedsalt stream 73 to the atomiser 210.

The atomiser 210 also receives filtered air.

The atomiser 210 makes use of a two fluid nozzle atomiser offeringco-current mode, but rotary atomisers and two fluid atomisers infountain mode are possible too. The high velocity air encounters the lowvelocity fluid to disintegrate that into droplets.

The atomiser 210 is positioned in the upper part of the drying chamber214, with the drying chamber 214 being formed of a cylindrical upperpart 216 and conical lower part 218. The bottom of the conical part 218provides the powder outlet 220 and moist air side outlet 222.

The atomised fluid directly encounters the hot air which has passedthrough the heating stage 212. The heating stage 212 includes theelectrical heat source and baffled air distributors to control the flowpattern and heat transfer in the air.

Upon entering the drying chamber 214 through the atomiser 210, thedissolved salt stream 73 comes into intimate contact with the hot air.This provides for the drying in the hot air stream. Away from theatomiser 210 the drying chamber 214 allows the separation of the drypowder from the hot air, with both passing to their respective outlets.

The dry powder is conveyed away by a fluidised ejector. Cooling andpacking of the powder can then be provided for.

The separated hot air enters an air stream going to atmosphere which isprovided with bag filters to remove any remaining powder, with cyclonesoffering an alternative form of filtering.

The following table defines some typical operating characteristics of asuitable spray dryer.

TABLE 1 Characteristic Value Units Processed material Chloride basedsalts Average residence time in dryer 11 s Material feed rate 100 Kg/hrFeed solids content 30 % Rate of powder production 30 Kg/hr Evaporationrate of dryer 70 Kg/hr Residual moisture in product 1 % Drying air inlettemperature 190 ° C. Drying air outlet temperature 97 ° C. Powdertemperature 85 ° C. Mass flow rate of drying air 2454 Kg/hr Heat inputto dryer 103905 Kcal/hr Heat input to dryer 120 KW Operational runningload 20 HP Electrical supply 440-3-50 VV-ph-Hz Instrumentation 24 V

The spray drying product has closely controlled particle sizedistribution, residual moisture content, bulk density and morphology

In terms of the results achieved, the variation in moisture contentachieved with varying conditions is detailed in Table 2.

TABLE 2 Feed Inlet Outlet Rate Salt Conc Moisture Trial Temp° C. Temp°C. L/hr wt % NaCl:KCl wt % 1 150 90 1.2 24.2 66:34 0.27 2 195 102 2 24.266:34 1.05 3 150 90 1.2 24.6 50:50 0.31 4 195 100 2 24.6 50:50 1.64 5150 90 1.2 16.7 66:34 0.32 6 196 102 2 16.7 66:34 7 150 90 1.2 17.049:51 1.18 8 197 99 2 17.0 49:51 1.40

The particles generated, when measured using SEM imaging, are generallyaround 5 to 30 microns in diameter and are blocky crystals inappearance. Optical microscope imaging also confirmed that the particlestend to form agglomerates of 120 to 2500 microns in diameter.

The pelletiser 99 is important in increasing the size of the product toa size at which it is not prone to airborne transportation out of thefurnace.

Roll based compactors were used to examine the suitability of the powderto pelletizing. The powder was fed using gravity through two counterrotating rollers. Friction between the material and the roller surfacesbrought the powder into the narrow space between the rolls and the highloads present gave good compaction of the powder. The powder heldtogether in the compacted form without the need for any binders, wateror other additives to be present.

Roll based pelletisers, where the rolls bear opposing halves of therecessed spaces where the pellets form where then used to form pelletssuccessfully.

The technique readily achieves moisture contents below 0.2 wt % andallows less than 2% of the material to be below 149 microns in diameter(so minimising the amount of fines present).

The invention claimed is:
 1. A method of processing a material, thematerial being the upper layer from a metal melting process, thematerial containing one or more salts, the material containing one ormore metals, the method including: a) feeding the material to a slagpress and compressing the material; b) feeding the compressed materialto a size reduction; wherein steps a) and b) are provided before thetemperature of the compressed material has reduced below 350° C.; themethod further including: c) reducing one or more dimensions of thecompressed material in the size reduction step, the size reduction stepincluding a crushing step; d) feeding the crushed material to a leachingstep; e) obtaining a leachate from the leaching step; f) feeding theleachate to a spray drying step; and g) obtaining a solid from the spraydrying step.
 2. A method according to claim 1 in which the leaching stepfurther provides one or more other outlet streams, including an off gasstream, the off gas stream being further processed by combustion, withheat and/or power generated by the combustion being used in the spraydrying step.
 3. A method according to claim 1 further comprising a stepfor feeding hot gas to the spray drying step, the hot gases being froman off gas stream processing and/or possessing energy generated by anoff gas stream processing.
 4. A method according to claim 1 includingthe further step of compressing and/or moulding the solid into pellets.5. A method according to claim 1 wherein the leaching step comprises amultiple pass leaching process where multiple passes through oneleaching tank are provided and/or a multiple stage leaching processwhere passage through a number of leaching tanks is provided.
 6. Amethod according to claim 1 including a step for obtaining a solid fromthe spray drying step, by separating the solid and a gas in the spraydrying step.
 7. A method according to claim 6 including a step forcompressing and/or moulding the solid into pellets in one or morefurther steps.
 8. A method according to claim 7 wherein the step forcompressing and/or moulding is provided without adding any furthercomponents to the solid.
 9. A method according to claim 7 wherein thecompressed and/or moulded solids are be fed to a furnace to provide amaterial on the surface of a molten metal in a furnace.
 10. A methodaccording to claim 7 wherein the compressed and/or moulded solids areproduced with a controlled ratio of sodium chloride to potassiumchloride.
 11. A method according to claim 7 wherein the step forcompressing and/or moulding solids is provided without adding anybinders or moisture.
 12. A method according to claim 1, wherein the oneor more salts are selected from sodium chloride, sodium chlorate,potassium chloride, or potassium chlorate.
 13. A method according toclaim 1 further comprising a step for the recycling of one or moremetals produced.
 14. A method according to claim 1, wherein steps a) andb) are provided before the temperature of the compressed material hasreduced below 525° C.
 15. A method according to claim 1 furthercomprising a step for recycling one or more salts produced.
 16. A methodaccording to claim 1 wherein the one or more metals are selected fromaluminium or aluminium oxide.
 17. A method according to claim 1 whereinsteps a) and b) are provided before the temperature of the compressedmaterial has reduced below 760° C.